Estimation of in-river fish passage using a combination of transect and stationary hydroacoustic sampling

Abstract

We describe a hydroacoustic technique that uses both transect and stationary sampling to estimate numbers of fish migrating in a river. The technique includes refinements and additions to one developed by the International Pacific Salmon Fisheries Commission to estimate sockeye (Oncorhynchus nerka) and pink salmon (Oncorhynchus gorbuscha) migrations in the Fraser River. The estimator is independent of the actual shape of the effective acoustic beam and the distribution of target strengths when the same hydroacoustic equipment and settings are used for both types of soundings. Thus, the method shares with the duration-in-beam method the advantages that equipment calibration requirements are minimal and that estimates remain valid when fish sizes vary over a wide range. We also provide formulae for the variance of the abundance estimate and illustrate the methods with example calculations of daily fish passage in the Fraser River at Mission, British Columbia. A correction procedure is proposed to compensate for bias arising from violation of the assumption that fish speed is negligible relative to boat speed.